The present invention relates generally to tiltable chairs, and in particular, to a tilt chair having a flexible back, adjustable armrests, and an adjustable seat depth, and methods for using and/or adjusting the chair, including one or more of the seat, backrest and armrests.
Chairs of the type typically used in offices and the like are usually configured to allow tilting of the seat and backrest as a unit, or to permit tilting of the backrest relative to the seat. In chairs having a backrest pivotally attached to a seat in a conventional manner, the movement of the backrest relative to the seat can create shear forces which act on the legs and back of the user, and which can also create an uncomfortable pulling of the user's shirt, commonly called “shirt-pull.”
To enhance the user's comfort and to promote ergonomically healthy seating, synchro-tilt chairs provide for the seat and backrest to tilt simultaneously, but at different rates, preferably with the back tilting at a greater rate than the seat. In general, synchro-tilt chairs are usually configured as a four-bar linkage or as a three-bar, slide linkage. In a three-bar, slide configuration, the sliding path is typically linear. Such chairs often have a multiplicity of components and parts that can be difficult and time consuming to assemble and which require multiple fasteners or joints to connect the components.
In addition, synchro-tilt chairs normally employ compression and/or tension springs, torsion springs and/or torsion bars, or leaf springs to bias the seat and back upwardly and to counterbalance the rearward tilting of the user. Chairs using these types of springs can have various limitations associated with the type of spring used therein as explained in U.S. Pat. No. 6,250,715, entitled Chair, and assigned to Herman Miller, Inc., the entire disclosure of which is hereby incorporated herein by reference. In addition, the mechanisms used to adjust the load on the spring(s), or the load capability of the spring(s), typically are complicated, and/or require multiple, excessive rotations of a knob or other grippable member to obtain the desired setting.
Often, such tilt chairs do not provide a balanced ride throughout the range of tilting motion of the chair. Specifically, the restoring force or torque of the chair, and in particular the spring, does not match the force or torque applied by the user throughout the tilting range. Although the applied force and restoring force may balance out at a particular tilt position, such balance does not typically occur throughout the tilting range. Moreover, such balance typically cannot be achieved for a variety of users having different weights and body sizes. As such, the user must exert energy and/or apply an external force to maintain the chair in a particular location.
It is also desirable to provide a chair that can be adjusted to accommodate the various needs and sizes of the user. For example, it is often desirable to provide a chair having adjustable armrests and an adjustable seat depth. For example, armrests can be provided with vertical adjustment capabilities, lateral adjustment capabilities and pivotable adjustment capabilities about a vertical axis. Often, however, armrests fail to provide such capabilities in combination, and/or employ complex, moving parts and assemblies that can be expensive to manufacture and assemble and difficult to use. Moreover, armrests having vertical adjustment capabilities often employ a support member that extends vertically down along the side of the chair, where the armrest or support member can interfere with the user's legs and other objects as the user moves about in the chair. In addition, the range of adjustment is typically limited to the length of the support member. However, the longer the support member, or the further it extends below the seating surface, the more likely it is to increase the foot print of the chair and interfere with the mobility of the chair.
Chairs with adjustable seat depths often employ devices and mechanisms to shift the entire seat in a forward and rearward direction relative to the backrest. Therefore, such chairs must provide for structure to allow the seat to move relative to the backrest while at the same time bearing the load of the seat and user. Moreover, such chairs typically must employ an extra support member which allows the seat to move thereon, for example, when the seat or support member are integrated into the linkage assembly.
Typically, backrests having a resilient and/or flexible material, whether a fabric, elastic membrane or plastic mat, are often supported by a peripheral frame, which surrounds the material. Such construction, however, does not ordinarily permit flexing of the material at the periphery of the backrest, or allow for torsional movement of the backrest. In addition, even in those chairs that employ a resilient material, the material often has uniform mechanical and physical properties across the entire portion of the material.
Finally, as disclosed for example in U.S. Pat. No. 5,873,634 to Heidmann et al., it is known to connect different seating arrangements to a control housing. However, Heidmann discloses connecting different seating arrangements to a tilt control housing and back support at common connection points. Accordingly, the overall kinematics of the chair cannot be altered or varied, but rather are predetermined by the common connection points. In such a device, only localized adjustments within each seating arrangement can be varied between the different seating arrangements.